In recent years, the X-ray CT apparatus provided with multi-energy scanning function has been developed capable of acquiring CT images by different effective photon energies by using a plurality of different tube voltages upon scanning the same tomographic plane or providing discriminating function of X-ray photon energies to an X-ray detector.
The advantage of the multi-energy scanning is that it is possible to distinguish the subjects, for example a bone and a contrast-filled blood vessel having proper concentration that are difficult to distinguish by a single effective energy since the CT values of the subjects are the same, by using different effective energies which makes the subjects have different CT values.
The configuration methods for the X-ray CT apparatus comprising the above-mentioned multi-energy scanning function will be described below and they are commonly-known in the Patent Documents to be listed below and in the meeting held by Radiological Society of North America in 2006.
(1) First Method
The X-ray CT apparatus is mounted with a plurality of pairs of an X-ray tube and an X-ray detector, so as to execute measurement by different tube voltages in each pair (hereinafter referred to as the multi-source/multilayered-detector method). This method is disclosed in Patent Document 1.
(2) Second Method
The X-ray detector is multilayered with respect to the transmitting direction of an X-ray so as to acquire the measurement data by different effective energies for each layer of the detector (hereinafter referred to as the multilayered detector method). This multilayered detector method is capable of multi-energy scanning without scanning by different tube voltages, and is disclosed in Patent Document 2.
(3) Third Method
This method comprises a pair of X-ray tubes and a non-multilayered X-ray detector so as to execute plural times of scanning with different tube voltages with respect to the same tomographic plane. The representative method irradiates an X-ray during ⅔ rotation in the first rotation after start of scanning, stops X-ray irradiation during the next ⅓ rotation so as to set the tube voltage different from the first scanning for the next scanning, and executes the next ⅔ rotation of scanning with the tube voltage set to be different from the first scanning (hereinafter referred to as the multi-half scanning method).
This method is disclosed in Non-patent Document 1 from the meeting Radiological Society of North America held in 2006.
Patent Document 1: Japanese Patent No. 3405760
Patent Document 2: JP-A-2001-174564
Non-patent Document 1: A. Ueno et al. “Evaluation and Assessment of Material Decomposition between Bone/Calcification and Iodine for CT Angiography Using 40 mm Coverage Volumetric CT with Novel High-Speed Pulsed Dual Energy Scanning”, Radiological Society of North America; Scientific Assembly and Annual Meeting Program 2006, pp 962, LL-VI2525